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Infection, Pharmacology & VTE MCQs

Practice Set 36 of 68

This practice set contains high-yield board review questions covering key concepts in Infection, Pharmacology & VTE. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 701

Topic: Infection, Pharmacology & VTE

In the lifecycle of a bacterial biofilm associated with orthopedic implants, what is the final stage that facilitates the spread of infection to new sites?

. Irreversible planktonic attachment
. Quorum sensing and matrix production
. Detachment and dispersal
. Intracellular invasion and host cell lysis

Correct Answer & Explanation

. Detachment and dispersal

Explanation

The biofilm lifecycle consists of initial attachment, irreversible adherence, matrix maturation, and finally, detachment or dispersal. During dispersal, clumps of bacteria or planktonic cells are released to seed new areas, propagating the infection.

Question 702

Topic: Infection, Pharmacology & VTE

A 14-month-old girl presents with a limp and refusal to bear weight on the right leg. She has a low-grade fever and a recent upper respiratory infection. Inflammatory markers are mildly elevated. Blood cultures are negative, but a joint aspiration of the knee grows a fastidious Gram-negative coccobacillus on blood agar. What is the most likely causative organism?

. Staphylococcus aureus
. Haemophilus influenzae type B
. Kingella kingae
. Streptococcus pneumoniae
. Neisseria meningitidis

Correct Answer & Explanation

. Kingella kingae

Explanation

Kingella kingae is a common cause of pediatric septic arthritis and osteomyelitis in children under 4 years old. It is a fastidious Gram-negative organism that often follows upper respiratory infections.

Question 703

Topic: Infection, Pharmacology & VTE

A 72-year-old male with an infected total hip arthroplasty undergoes a two-stage revision. During the extraction of the components, thick biofilm is noted on the prosthesis. Which of the following describes the primary characteristic of the bacteria within the deeper layers of this biofilm?

. High metabolic activity and rapid replication
. Exclusively Gram-negative organisms
. Decreased metabolic rate and resistance to standard antibiotics
. Planktonic state with high susceptibility to beta-lactams
. Lack of an extracellular polymeric substance (EPS) matrix

Correct Answer & Explanation

. Decreased metabolic rate and resistance to standard antibiotics

Explanation

Bacteria embedded deep within a biofilm enter a stationary phase with a lowered metabolic rate (persister cells). This makes them highly recalcitrant to traditional antibiotics that target actively dividing cells.

Question 704

Topic: Infection, Pharmacology & VTE

A 12-year-old boy is diagnosed with acute hematogenous osteomyelitis of the proximal tibia. Cultures grow Methicillin-resistant Staphylococcus aureus (MRSA). The patient has a known severe anaphylactic allergy to vancomycin. Which of the following intravenous antibiotics is the most appropriate alternative for targeting the MRSA?

. Cefazolin
. Clindamycin
. Daptomycin
. Ceftriaxone
. Ampicillin-sulbactam

Correct Answer & Explanation

. Daptomycin

Explanation

Daptomycin is an excellent bactericidal alternative for MRSA in patients with vancomycin allergies or intolerance. Clindamycin resistance in MRSA is increasing and depends on local antibiograms, making daptomycin a more reliable empiric IV choice.

Question 705

Topic: Infection, Pharmacology & VTE

A 22-year-old sexually active female presents with acute onset of right knee pain, swelling, and fever. She also reports migrating polyarthralgia over the past three days and a few painless pustular skin lesions on her hands. Synovial fluid aspiration shows 45,000 WBC/uL. What is the most likely pathogen?

. Staphylococcus aureus
. Neisseria gonorrhoeae
. Streptococcus pyogenes
. Borrelia burgdorferi
. Treponema pallidum

Correct Answer & Explanation

. Neisseria gonorrhoeae

Explanation

Disseminated gonococcal infection classically presents in young, sexually active patients with migratory polyarthritis, tenosynovitis, and painless pustular dermatitis. Synovial WBC counts may be lower than those seen in staphylococcal septic arthritis.

Question 706

Topic: Infection, Pharmacology & VTE
A 2-year-old child presents with a limp, low-grade fever, and refusal to bear weight on the right leg. Hip aspiration yields synovial fluid with a WBC count of 45,000 cells/uL. Standard Gram stain and routine cultures are negative at 48 hours. What is the most appropriate method to identify the most likely causative organism?
. Acid-fast bacilli smear
. Darkfield microscopy
. Inoculation of synovial fluid directly into BACTEC blood culture vials or PCR testing
. Fungal cultures on Sabouraud dextrose agar
. Enzyme-linked immunosorbent assay (ELISA) for Lyme disease

Correct Answer & Explanation

. Inoculation of synovial fluid directly into BACTEC blood culture vials or PCR testing

Explanation

Kingella kingae is the most common cause of septic arthritis in children under 4 years old. It is a fastidious organism that is notoriously difficult to grow on solid media; inoculation into blood culture vials or PCR significantly increases detection.

Question 707

Topic: Infection, Pharmacology & VTE

A 7-year-old boy with sickle cell disease presents with fever, focal tibial pain, and swelling. While Staphylococcus aureus remains the most common overall cause of osteomyelitis in this population, which of the following organisms is disproportionately more prevalent in patients with this underlying disease compared to the general pediatric population?

. Pseudomonas aeruginosa
. Streptococcus pneumoniae
. Salmonella typhimurium
. Kingella kingae
. Haemophilus influenzae

Correct Answer & Explanation

. Salmonella typhimurium

Explanation

Patients with sickle cell disease have functional asplenia and a uniquely high susceptibility to Salmonella osteomyelitis, although S. aureus still remains the most common cause overall.

Question 708

Topic: Infection, Pharmacology & VTE
A 4-year-old boy presents with an acute onset of a limp and refuses to bear weight on his right leg. His temperature is 38.8°C (101.8°F). Laboratory tests show a WBC count of 13,500/mm³ and an ESR of 55 mm/hr. According to the Kocher criteria, what is the predictive probability that this child has septic arthritis of the hip?
. Less than 10%
. Approximately 40%
. Approximately 71%
. Approximately 93%
. Greater than 99%

Correct Answer & Explanation

. Greater than 99%

Explanation

The patient has all four Kocher criteria (non-weight-bearing, fever >38.5°C, WBC >12,000, ESR >40). The presence of all 4 criteria yields a 99% probability of septic arthritis.

Question 709

Topic: Infection, Pharmacology & VTE

Which of the following organisms is most heavily reliant on the production of a polysaccharide glycocalyx (slime layer) to adhere to orthopedic implants and evade host immune responses in chronic periprosthetic joint infections?

. Streptococcus pyogenes
. Escherichia coli
. Staphylococcus epidermidis
. Pseudomonas aeruginosa
. Propionibacterium acnes

Correct Answer & Explanation

. Staphylococcus epidermidis

Explanation

Staphylococcus epidermidis is notorious for forming a thick glycocalyx biofilm on foreign bodies, which facilitates adherence and protects the bacteria from both systemic antibiotics and host phagocytosis.

Question 710

Topic: Infection, Pharmacology & VTE

During surgical debridement of chronic osteomyelitis, the surgeon removes a piece of dense, isolated bone. By definition, a sequestrum represents which of the following?

. New reactive bone forming a shell around an infection
. An area of localized, unmineralized osteoid
. A segment of necrotic bone separated from living bone
. A walled-off abscess cavity within cancellous bone
. Calcified granulation tissue within the medullary canal

Correct Answer & Explanation

. A segment of necrotic bone separated from living bone

Explanation

In chronic osteomyelitis, a sequestrum is a piece of dead, necrotic bone that has become separated from the surrounding living bone. An involucrum is the shell of new reactive bone forming around it.

Question 711

Topic: Infection, Pharmacology & VTE

A 2-week-old neonate presents with pseudoparalysis of the right leg and irritability with diaper changes. Ultrasound shows a hip effusion and radiographs reveal subtle changes as shown.

Besides Staphylococcus aureus, which organism is a leading cause of septic arthritis in this age group?

. Streptococcus pneumoniae
. Group B Streptococcus
. Kingella kingae
. Haemophilus influenzae type B
. Neisseria gonorrhoeae

Correct Answer & Explanation

. Group B Streptococcus

Explanation

Group B Streptococcus and Staphylococcus aureus are the most common pathogens responsible for neonatal septic arthritis. Neonates often lack systemic signs like fever, presenting instead with pseudoparalysis.

Question 712

Topic: Infection, Pharmacology & VTE
A 3-year-old boy is diagnosed with Kingella kingae septic arthritis of the knee. What is the most effective method for isolating this fastidious organism from synovial fluid?
. Plating directly onto MacConkey agar
. Inoculation into aerobic blood culture vials (BACTEC)
. Fungal culture medium
. Acid-fast bacillus smear
. Viral transport medium

Correct Answer & Explanation

. Inoculation into aerobic blood culture vials (BACTEC)

Explanation

Kingella kingae is a fastidious, Gram-negative organism that is difficult to culture on standard solid media. Inoculating the synovial fluid directly into aerobic blood culture vials (BACTEC) significantly increases the diagnostic yield.

Question 713

Topic: Infection, Pharmacology & VTE

A 7-year-old girl from Massachusetts presents with a massive, painless effusion of her right knee. She is afebrile and inflammatory markers are minimally elevated. Joint aspiration yields 45,000 WBCs/microL. After sending synovial fluid for testing, what is the recommended initial management for this likely diagnosis?

. Urgent arthroscopic irrigation and debridement
. Oral doxycycline for 14 days
. Oral amoxicillin for 28 days
. Intra-articular corticosteroid injection
. Intravenous vancomycin and ceftriaxone

Correct Answer & Explanation

. Oral amoxicillin for 28 days

Explanation

This is a classic presentation of Lyme arthritis (large, relatively painless effusion, low-grade inflammatory markers in an endemic area). For children under 8 years of age, a 28-day course of oral amoxicillin is the standard treatment to avoid the tooth-staining side effects of doxycycline.

Question 714

Topic: Infection, Pharmacology & VTE
An 18-month-old child presents with a limp and low-grade fever. Hip aspiration yields purulent fluid with a normal Gram stain. Routine cultures are initially negative, but growth is eventually achieved using aerobic blood culture vials (BACTEC). What is the most likely causative organism?
. Staphylococcus aureus
. Streptococcus pyogenes
. Kingella kingae
. Haemophilus influenzae
. Salmonella enterica

Correct Answer & Explanation

. Kingella kingae

Explanation

Kingella kingae is a fastidious Gram-negative organism that is now recognized as the most common cause of septic arthritis in children younger than 4 years. It often requires inoculation into blood culture vials for successful growth.

Question 715

Topic: Infection, Pharmacology & VTE

A 9-year-old boy presents with severe thigh pain, high fever, and a swollen, erythematous leg. MRI confirms osteomyelitis of the femur and an adjacent deep venous thrombosis (DVT). Blood cultures grow gram-positive cocci. Which of the following virulence factors is most strongly associated with this severe clinical presentation?

. Toxic shock syndrome toxin-1 (TSST-1)
. Protein A
. Panton-Valentine leukocidin (PVL)
. Coagulase
. Streptolysin O

Correct Answer & Explanation

. Panton-Valentine leukocidin (PVL)

Explanation

Panton-Valentine leukocidin (PVL) is a cytotoxin frequently produced by community-acquired MRSA. It is associated with severe musculoskeletal infections, multifocal osteomyelitis, adjacent myositis, and deep venous thrombosis.

Question 716

Topic: Infection, Pharmacology & VTE

A 7-year-old girl with homozygous sickle cell disease (HbSS) presents with severe bone pain, high fever, and swelling over the midshaft of her radius. MRI confirms diaphyseal osteomyelitis. While Staphylococcus aureus is highly prevalent, this patient is uniquely at high risk for infection from which of the following organisms?

. Pseudomonas aeruginosa
. Salmonella typhimurium
. Streptococcus pneumoniae
. Haemophilus influenzae
. Neisseria meningitidis

Correct Answer & Explanation

. Salmonella typhimurium

Explanation

While Staphylococcus aureus is still the most common cause of osteomyelitis in the general pediatric population and very common in sickle cell disease, patients with sickle cell hemoglobinopathies are at uniquely high risk for Salmonella osteomyelitis.

Question 717

Topic: Infection, Pharmacology & VTE
An 18-month-old child presents with a limp, low-grade fever, and refusal to bear weight. Blood labs show CRP 25 mg/L and WBC 11,000/mm3. Standard synovial fluid culture is negative at 48 hours. To isolate the most likely causative organism in this age group, which laboratory technique should have been utilized?
. Fungal culture on Sabouraud agar
. Acid-fast bacilli smear
. Inoculation of synovial fluid into BACTEC aerobic blood culture vials
. Addition of hypertonic saline to the growth medium
. Polymerase chain reaction for Borrelia burgdorferi

Correct Answer & Explanation

. Inoculation of synovial fluid into BACTEC aerobic blood culture vials

Explanation

Kingella kingae is the most common cause of septic arthritis in children under 4 years old. It is a fastidious Gram-negative organism; inoculating synovial fluid into BACTEC aerobic blood culture vials or utilizing PCR significantly increases diagnostic yield.

Question 718

Topic: Infection, Pharmacology & VTE

A 9-year-old girl presents with multiple recurrent episodes of bone pain and swelling in her clavicle and distal tibia. Labs show a mildly elevated ESR but normal WBC count. Multiple biopsies reveal sterile, non-infectious inflammation. What is the first-line treatment for this condition?

. Intravenous antibiotics for 6 weeks
. Surgical debridement of all lesions
. Nonsteroidal anti-inflammatory drugs (NSAIDs)
. Oral corticosteroids
. Methotrexate

Correct Answer & Explanation

. Nonsteroidal anti-inflammatory drugs (NSAIDs)

Explanation

Chronic Recurrent Multifocal Osteomyelitis (CRMO) is an autoinflammatory bone disorder characterized by sterile bone lesions. NSAIDs are the first-line treatment, successfully controlling symptoms in the majority of patients.

Question 719

Topic: Infection, Pharmacology & VTE

A 3-week-old neonate presents with a swollen, erythematous right thigh and pseudoparalysis. An ultrasound confirms a hip effusion, and radiographs show early destructive changes in the proximal femur.

What anatomic factor strongly predisposes neonates to concurrent osteomyelitis and septic arthritis of the hip?

. Presence of transphyseal vessels
. Avascular necrosis of the capital femoral epiphysis
. Thickened, impermeable periosteum
. Delayed ossification of the femoral head
. Absence of a joint capsule

Correct Answer & Explanation

. Presence of transphyseal vessels

Explanation

In infants younger than 18 months, transphyseal blood vessels cross the physis. This allows hematogenous infection to easily spread between the metaphysis and the epiphysis or joint space, causing concurrent osteomyelitis and septic arthritis.

Question 720

Topic: Infection, Pharmacology & VTE
A 7-year-old boy from Connecticut presents with acute right knee swelling and a limp. He is afebrile with a WBC of 9,000/mm³ and an ESR of 30 mm/hr. Joint aspiration yields 45,000 WBCs/mm³ with a predominance of PMNs. What is the most appropriate next step in diagnosis?
. Immediate arthroscopic irrigation and debridement
. Lyme serology (ELISA followed by Western blot)
. Intravenous vancomycin and ceftriaxone
. Open arthrotomy
. Technetium-99m bone scan

Correct Answer & Explanation

. Lyme serology (ELISA followed by Western blot)

Explanation

In a Lyme-endemic area, a child with monoarticular knee effusion, low inflammatory markers, and a moderate joint WBC count often has Lyme arthritis. Testing with two-tiered Lyme serology is indicated before considering surgical intervention.

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